How do I resolve the deprecation warning "Method to_hash is deprecated and will be removed in Rails 5.1"

I'm trying to update to Rails 5, I'm getting the following deprecation warning:

DEPRECATION WARNING: Method to_hash is deprecated and will be removed in Rails 5.1, as

ActionController::Parameters

no longer inherits from hash. Using this deprecated behavior exposes potential security problems. If you continue to use this method you may be creating a security vulnerability in your app that can be exploited. Instead, consider using one of these documented methods which are not deprecated: http://api.rubyonrails.org/v5.0.0/classes/ActionController/Parameters.html (called from column_header at /Data/Projects/portal/trunk/app/helpers/application_helper.rb:114)